Abstract: The Adirondack Manipulation and
Modeling Project (AMMP) was initiated in 1990 to investigate the
effects of changing chemical inputs in the Adirondack Mountains
of New York (USA). The four study sites are located across a west
to east gradient of declining atmospheric deposition, increasing
acid neutralizing capacity (ANC) and decreasing NO3-
concentration in surface waters in the Adirondacks. We
hypothesize that the two sites in the western Adirondacks (Wood
Lake (WL) and Pancake-Hall (PCH) ) exhibit lower critical loads
of N, S and H+ than the central and eastern sites
(Huntington Forest (HF) and Pack Forest (PF), respectively). To
test this hypothesis, chemical treatments of plots were initiated
in 1990 including (NH4)2SO4 (1000 and 2000
eq ha -1 year -1), H2SO4 (1000
eq ha-1 year-1), HNO3 (1000 eq ha-1 year-1), Ca+Mg+SO42-
(1000 eq ha-1 year-1). Three of the sites (WL, PHC and HF) are
northern hardwood ecosystems underlain by Spodosols. The PF site
is a Pinus resinosa plantation on a glacial outwash
plain (Typic Udipsamment). Ions in total deposition, throughfall
and soil leachates are monitored continuously. Changes in the
solid phase chemistry of the mineral soil were assessed annually
using the buried soil-bag approach. Vegetation responses to
chemical treatments were analyzed by ascertaining changes in
growth, composition and nutrient concentrations of both the
overstory and understory. Elemental cycling models used in the
AMMP include NuCM and VEGIE-CHESS.

Preliminary results of bulk precipitation and throughfall from
1991-1992 suggest that the western sites may have greater inputs
of SO42- and have lower capacity to retain
NO3- passing through the foliage. Soil
solutions (1991-1992) in reference plots of the western sites (WL
and PHC) had higher concentrations of NO3-
in soil solution then the central and eastern Adirondack sites
(HF and PF). For all sites except PF, ammonium sulfate additions
resulted in increased concentrations of SO42-
and NO3- in soil solutions. Results of
model simulations with NuCM for HF are presented which suggest
that the model adequately simulated the pattern of increasing SO42-
concentrations in response to (NH4)2SO4
treatment, but that the increase in NO3-
was underestimated.